RU2238337C1 - Method for producing of rolled bars from low carbon steel for cold bulk pressing of compound-shaped fastening parts - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves melting steel in electric furnace; processing beyond furnace; pouring in casting molds while protecting metal flow; hot rolling of ingot for producing of blank, with following rolling thereof and controlled cooling and winding of rolled product into rolls; melting steel containing, wt%: carbon 0.17-0.25; manganese 0.30-0.65; silicon 0.01-0.17; sulfur 0.005-0.020; vanadium 0.005-0.07; niobium 0.005-0.02; calcium 0.001-0.010, with following ratio being met: 12/C-Mn/0.02≥27; 0.46≥6xV+8xNb≥0.22; Ca/S≥0.065. Steel microalloying with niobium inhibits steel recrystallization processes at rolling final temperature of 1,00⁰-1,050⁰C. Hot rolling of bars is completed at temperature of 1,000-1,050⁰C, with following accelerated cooling to temperature of 750-850⁰C and rolling at deformation extent of at least 30% with following cooling in air to temperature of 300⁰C.

EFFECT: provision for producing of rolled bars with structure allowing adequate cold bulk pressing conditions to be created without additional spheroidizing annealing process and improved steel deformability characteristics.

2 cl, 2 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products from low carbon steel for cold die forging fasteners of particularly complex shapes.

Known structural steel, containing, wt.%: Carbon 0.18-0.22%, manganese 0.27-0.67%, silicon 0.17-0.37%, vanadium 0.05-0.10%, niobium 0.01-0.04%, the rest is iron, in the following ratio of components, wt. %: 6V + 8Nb≥ 0.56 and 100000VNb ² ≤ 8.0 (USSR copyright certificate 1772208 of 10.30.1992 Bull. No. 40, C 22 C 38/12).

The most important requirement for long products from low carbon steel for cold forming for fasteners of especially complex shape is, on the one hand, high technological ductility and low coefficient of strain hardening in the delivery state and, on the other hand, the ability to provide a given level of consumer properties after cold forging. This steel from the batch to the finished long products undergoes a fairly lengthy redistribution, which includes the following operations: smelting, hot rolling, spheroidizing annealing, calibration. The task of providing the necessary set of mechanical properties, indicators of technological plasticity and a low coefficient of strain hardening of rolled metal in the delivery state is currently being successfully solved by a number of techniques used at various stages of steelmaking.

The objective of the invention is the development of steel with increased stampability and a method for the production of long products from it, which ensures the production of high quality steel directly in the mill stream (without additional spheroidizing annealing). The technical result of the invention is to obtain a rental structure that guarantees rational conditions for cold forming for complex profile fasteners.

The closest analogue to the claimed invention is a known method for the production of long products from low carbon steel for cold forming for fasteners, including steelmaking in an electric furnace, out-of-furnace processing, casting into molds, hot rolling of an ingot and cooling (RU 2156311 C1, C 21 D 8 / 12, September 20, 2000).

To achieve a technical result in the known method for the production of long products from low carbon steel for cold forging of fasteners, including steelmaking in electric furnaces, after-furnace treatment, casting into molds, hot rolling of the ingot and cooling, steel is melted in the following ratio of components, wt.%:

Carbon 0.17-0.25

Manganese 0.30-0.65

Silicon 0.01-0.17

Sulfur 0.005-0.020

Vanadium 0.005-0.07

Niobium 0.005-0.02

Calcium 0.001-0.010

Iron Else

when the relations

0.46≥ 6× V+8× Nb≥ 0,22;

0.46≥ 6 × V + 8 × Nb≥ 0.22;

hot rolling is completed at 1000-1050 ° C, rapidly cooled to 750-850 ° C and rolled with a degree of deformation of at least 30%, followed by cooling in air. When casting steel into molds, a stream of metal is protected by argon.

The given combinations of alloying elements (item 1) make it possible to obtain directly in the state of supply of a spheroidized structure in the proposed carbon steel (bar with a diameter of up to 25 mm) that provides rational conditions for the cold forging of complex-profile parts and provides a favorable combination of strength and ductility characteristics.

Carbon and carbonitride-forming elements (vanadium, niobium) are introduced into the composition of this steel in order to provide a fine grain structure, which will increase both its strength level and provide a given level of ductility. At the same time, niobium and vanadium control processes in the austenitic region (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical processing, increases the temperature of recrystallization and, as a result, affects the nature of the γ -α transformation. Niobium and vanadium also contributes to the hardening of steel upon thermal improvement The upper limit of carbon content (0.25%), niobium (0.02%) and vanadium (0.07%) is due to the need to ensure the required level of ductility of steel, and the lower - 0.17%, 0.005% and 0.005%, respectively - rebuemogo strength level of the steel.

Manganese is used, on the one hand, as a hardener of a solid solution, and on the other hand, as an element that significantly increases the stability of supercooled austenite. Moreover, the upper level of manganese content of 0.65% is determined by the need to ensure the required level of ductility of steel, and the lower 0.30% by the need to provide the required level of strength of steel.

Silicon refers to ferrite-forming elements. The lower silicon limit of 0.01% is due to steel deoxidation technology. A silicon content above 0.17% will adversely affect the ductility characteristics of steel. Sulfur determines the level of ductility of steel. The upper limit (0.020%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.005%) is due to issues of manufacturability.

Calcium is an element that modifies non-metallic inclusions. The upper limit (0.010%), as in the case of sulfur, is due to the need to obtain a given level of ductility and toughness of steel, and the lower (0.001%) limit is due to issues of manufacturability.

0.46≥ 6× V+8× Nb≥ 0,22;

The ratio

0.46≥ 6 × V + 8 × Nb≥ 0.22;

determine the conditions for ensuring the specified characteristics of ductility and hardenability of steel during cold forging of complex profile fasteners. Below are examples of the implementation of the invention, not excluding others, in the scope of the claims.

Smelting of low-carbon steel of the following composition: carbon 0.21%, manganese 0.45%, silicon 0.10%, chromium 0.20%, sulfur 0.011%, vanadium 0.03%, niobium 0.01%, calcium 0.001%, is carried out in the Fuchs mine. For a guaranteed low nitrogen content, a special technology has been developed, which includes melting batch with molten iron up to 40% of the total charge volume. The oxidation period provides for high rates of carbon oxidation in the range of 0.05-0.07% / min. The electric mode provides for turning off the furnace with a carbon content of 0.2-0.4% above the lower limit for a given one, carbon blowing is carried out without an electric arc. The temperature of the outlet from the furnace is 1640-1680 ° С. Ferroalloys are introduced, steel is treated to remove non-metallic inclusions at the ladle furnace equipped with an electric heating or chemical heating system. The temperature of the steel before casting is 60 ° C higher than the liquidus temperature of the brand. Steel is cast in molds widened to the top. The weight of the ingot is 7.85 tons. To ensure a low nitrogen content during casting, the metal stream is protected by argon through a special ring device. The ingots are heated in a crimping workshop in recuperative wells to a rolling start temperature of 1250-1270 ° C. The ingots are rolled in blooming (mill 1300) and then on a continuous billet mill for a workpiece with a section of 100 × 100 mm. To remove the decarburized layer formed during heating of the ingots, the workpieces are subjected to abrasive cleaning. Then, the obtained workpiece was hot rolled at wire mill 150 or small mill 250 in diameters from 5.5 to 23 mm in coils. To ensure the size of the decarburized layer is not more than 1% of the diameter, the rate of delivery of billets from the furnace is limited to not less than 100 t / h for mill 150 and not less than 56 t / h for mill 250. The temperature of the start of rolling of billets is 1220-1240 ° C for mill 250 and 1270-1290 ° C for mill 150. Hot rolling of long products is completed at a temperature of 1000-1050 ° C, then accelerated cooling to 750-850 ° C, rolled with a degree of deformation of at least 30%, followed by cooling in air to 300 ° C and subsequent winding in riots.

Fulfillment of the ratio of alloying elements made it possible to provide the required level of ductility of steel directly in the hot-rolled state at a level of δ = 25% and the level of cold precipitation of a sample with a diameter of 20 mm at 75% of the height.

при содержании марганца - 0.45%, углерода - 0.21%

when the manganese content is 0.45%, carbon is 0.21%

6 × V + 8 × Nb = 0.26 with a vanadium content of 0.03%, niobium - 0.01%

при содержании серы - 0.011%, кальция - 0.001%.

when the sulfur content is 0.011%, calcium is 0.001%.

Implementation of the proposed method for the production of long products from steel of increased stampability, which ensures that the structure of long products directly in the mill stream (without additional spheroidizing annealing) is obtained, which guarantees rational conditions for cold forging of complex-profile high-strength fasteners.

Claims (2)

1. Method for the production of long products from low carbon steel for cold forging of fasteners, including steelmaking in an electric furnace, out-of-furnace processing, casting steel into molds, hot rolling of an ingot, cooling, characterized in that steel is smelted in the following ratio of components, wt.% : Carbon 0.17-0.25 Manganese 0.30-0.65 Silicon 0.01-0.17 Sulfur 0.005-0.020 Vanadium 0.005-0.07 Niobium 0.005-0.02 Calcium 0.001-0.010 Iron Else when the relations

0.46≥6 × V + 8 × Nb≥0.22;

where C is carbon; Mn is manganese; V is vanadium; Nb is niobium; Ca is calcium; S is sulfur hot rolling is completed at a temperature of 1000-1050 ° C, rapidly cooled to 750-850 ° C and rolled with a degree of deformation of at least 30%, followed by cooling in air to 300 ° C. 2. The method according to claim 1, characterized in that when casting steel into the molds, they protect the stream of metal with argon.